Western barbastelle

Barbastelles roost in splits or behind loose bark of trees all year, generally in mature deciduous forests, as well as rock crevices[8] and within human buildings. In central Italy, tall dead beech in unmanaged woodland were found to be preferred as roost trees.[9] While barbastelles typically remain within a single roosting area, they move between individual roosts with great frequency.[1]

Barbastelles migrate to underground roosting sites over the winter, although they may stay within arboreal roosts in the beginning of the season. Winter roosting sites include natural caves and human structures such as basements, mines and bunkers. Barbastelles are relatively resistant to cold conditions, and are typically found hibernating in cold sites and in exposed positions.[1][10]

Barbastelles feed chiefly on moths, as well as on flies.[1][10][11] Research from Switzerland showed that the biologically most productive parts of the forest are exploited in priority by this species while hunting [8] and that ca. 99% of prey by volume consisted of Lepidoptera. More recent studies confirmed this predominance of Lepidoptera, underlining that medium-sized and larger specimens are targeted in priority by the barbastelles. However, seasonal diet changes were recorded during autumn due to potential interspecific competition (with Plecotus austriacus) and strong decrease of flying larger moths.[12]

The diet of the barbastelles appears to be one of the narrowest among European bats. This specialization in foraging habits probably points to a higher vulnerability of this species to negative changes in the abundance of moth populations. This could explain its current rarity throughout most of its range.[13]

While foraging, barbastelles behave as typical aerial-hawking bat species despite the fact that they hunt exclusively just above the forest canopy. This peculiar foraging technique could be explained by the co-evolution with the defence system of its prey.[13]

Specimens can travel up to 20 km per night for foraging purposes and nonreproductive females forage at greater distances than reproductive females [14]

Individuals reach their sexual maturity after one or two years. After total sexual segregation during most of spring and summer, the mating period starts at the end of summer, sometimes during swarming episodes. The mating period is often finishing with the start of the hibernation, but some cases of late mating during winter and early spring have been observed[15]

Around May–June, each pregnant female gives birth to 1 or 2 newborn juveniles which she breastfeeds up to 6 weeks.[16]

The barbastelle has two main call types used for echolocation. The frequency parameters of call type 1 lie between 30 and 38 kHz, have most energy at 33 kHz and have an average duration of 2.5 ms. The frequency parameters of call type 2 lie between 29 and 47 kHz, have most energy at 38 kHz and have an average duration of 4.1 ms.[17][18][19]

Major prey for the bat order Chiroptera is the moth order Lepidoptera. To minimize the risk of the bats' echolocation, moths (and in rarest examples, butterflies) have evolved to detect the echolocation calls of hunting bats, and use evasive flight manoeuvres, or reply with their own ultrasonic clicks to confuse the bat's echolocation. The Arctiidae subfamily of Noctuid moths uniquely respond to bat echolocation with three prevailing mechanisms: startle, sonar jamming, and acoustic aposematic defence. All these defences depend on specific environmental settings and the type of echolocation call; however, these responses are not mutually exclusive and can be used by the same moth for defence.[20]

In response some bat families are known to use clicks at frequencies above or below moths' hearing ranges. This is known as the allotonic frequency hypothesis. It argues that the auditory systems in moths have driven their bat predators to use higher or lower frequency echolocation to circumvent the moth hearing. Barbastelle bats have evolved to use a quieter mode of echolocation, calling at a reduced volume and further reducing the volume of their clicks as they close in on prey moths. The lower volume of clicks reduces the effective successful hunting range, but results in a significantly higher number of moths caught than other, louder bat species. Moths have further evolved the ability to discriminate between high and low echolocation click rates, which indicates whether the bat has just detected their presence or is actively pursuing them. This allows them to decide whether or not defensive ultrasonic clicks are worth the time and energy expenditure.

This species is classified as Near Threatened (NT) in the worldwide IUCN Red List,[1] while it is considered as Vulnerable (VU) at the European and European Union scale [31] and Near Threatened (NT) in the Mediterranean Red List.[32]